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  <div class="edit"><a href="https://gem5.googlesource.com/public/gem5-website/+/refs/heads/master/README.md">Edit this page</a></div>
  <b>authors:</b> Jason Lowe-Power<br>
  

  <br>
  <h1 id="garnet-synthetic-traffic">Garnet Synthetic Traffic</h1>

<p>The Garnet Synthetic Traffic provides a framework for simulating the <a href="/documentation/general_docs/ruby/garnet-2">Garnet network</a> with controlled inputs. This is useful for network testing/debugging, or for network-only simulations with synthetic traffic.</p>

<p><strong>Note: The garnet synthetic traffic injector only works with the <a href="/documentation/general_docs/ruby/Garnet_standalone.md">Garnet_standalone</a> coherence protocol.</strong></p>

<h2 id="related-files">Related files</h2>

<ul>
  <li>configs/example/garnet_synth_traffic.py: file to invoke the network tester</li>
  <li>src/cpu/testers/garnet_synthetic_traffic: files implementing the tester.
    <ul>
      <li>GarnetSyntheticTraffic.py</li>
      <li>GarnetSyntheticTraffic.hh</li>
      <li>GarnetSyntheticTraffic.cc</li>
    </ul>
  </li>
</ul>

<h2 id="how-to-run">How to run</h2>

<p>First build gem5 with the <a href="/documentation/general_docs/ruby/Garnet_standalone.md">Garnet_standalone</a> coherence protocol. The Garnet_standalone protocol is ISA-agnostic, and hence we build it with the NULL ISA.</p>

<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>scons build/NULL/gem5.debug PROTOCOL=Garnet_standalone

</code></pre></div></div>
<p>Example command:</p>

<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>./build/NULL/gem5.debug configs/example/garnet_synth_traffic.py  \
        --num-cpus=16 \
        --num-dirs=16 \
        --network=garnet2.0 \
        --topology=Mesh_XY \
        --mesh-rows=4  \
        --sim-cycles=1000 \
        --synthetic=uniform_random \
        --injectionrate=0.01
</code></pre></div></div>

<h2 id="parameterized-options">Parameterized Options</h2>

<table>
  <thead>
    <tr>
      <th><strong>System Configuration</strong></th>
      <th><strong>Description</strong></th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td><strong>–num-cpus</strong></td>
      <td>Number of cpus. This is the number of source (injection) nodes in the network.</td>
    </tr>
    <tr>
      <td><strong>–num-dirs</strong></td>
      <td>Number of directories. This is the number of destination (ejection) nodes in the network.</td>
    </tr>
    <tr>
      <td><strong>–network</strong></td>
      <td>Network model: simple or garnet2.0. Use garnet2.0 for running synthetic traffic.</td>
    </tr>
    <tr>
      <td><strong>–topology</strong></td>
      <td>Topology for connecting the cpus and dirs to the network routers/switches. More detail about different topologies can be found (here)[Interconnection_Network#Topology].</td>
    </tr>
    <tr>
      <td><strong>–mesh-rows</strong></td>
      <td>The number of rows in the mesh. Only valid when ‘’–topology’’ is ‘‘Mesh_<em>’’ or ‘‘MeshDirCorners_</em>’’.</td>
    </tr>
  </tbody>
</table>

<table>
  <thead>
    <tr>
      <th><strong>Network Configuration</strong></th>
      <th><strong>Description</strong></th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td><strong>–router-latency</strong></td>
      <td>Default number of pipeline stages in the garnet router. Has to be &gt;= 1.  Can be over-ridden on a per router basis in the topology file.</td>
    </tr>
    <tr>
      <td><strong>–link-latency</strong></td>
      <td>Default latency of each link in the network. Has to be &gt;= 1.  Can be over-ridden on a per link basis in the topology file.</td>
    </tr>
    <tr>
      <td><strong>–vcs-per-vnet</strong></td>
      <td>Number of VCs per Virtual Network.</td>
    </tr>
    <tr>
      <td><strong>–link-width-bits</strong></td>
      <td>Width in bits for all links inside the garnet network. Default = 128.</td>
    </tr>
  </tbody>
</table>

<table>
  <thead>
    <tr>
      <th><strong>Traffic Injection</strong></th>
      <th><strong>Description</strong></th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td><strong>–sim-cycles</strong></td>
      <td>Total number of cycles for which the simulation should run.</td>
    </tr>
    <tr>
      <td><strong>–synthetic</strong></td>
      <td>The type of synthetic traffic to be injected. The following synthetic traffic patterns are currently supported: ‘uniform_random’, ‘tornado’, ‘bit_complement’, ‘bit_reverse’, ‘bit_rotation’, ‘neighbor’, ‘shuffle’,  and ‘transpose’.</td>
    </tr>
    <tr>
      <td><strong>–injectionrate</strong></td>
      <td>Traffic Injection Rate in packets/node/cycle. It can take any decimal value between 0 and 1. The number of digits of precision after the decimal point can be controlled by ‘’–precision’’ which is set to 3 as default in ‘‘garnet_synth_traffic.py’’.</td>
    </tr>
    <tr>
      <td><strong>–single-sender-id</strong></td>
      <td>Only inject from this sender. To send from all nodes, set to -1.</td>
    </tr>
    <tr>
      <td><strong>–single-dest-id</strong></td>
      <td>Only send to this destination. To send to all destinations as specified by the synthetic traffic pattern, set to -1.</td>
    </tr>
    <tr>
      <td><strong>–num-packets-max</strong></td>
      <td>Maximum number of packets to be injected by each cpu node. Default value is -1 (keep injecting till sim-cycles).</td>
    </tr>
    <tr>
      <td><strong>–inj-vnet</strong></td>
      <td>Only inject in this vnet (0, 1 or 2). 0 and 1 are 1-flit, 2 is 5-flit. Set to -1 to inject randomly in all vnets.</td>
    </tr>
  </tbody>
</table>

<h2 id="implementation-of-garnet-synthetic-traffic">Implementation of Garnet synthetic traffic</h2>
<p>The synthetic traffic injector is implemented in GarnetSyntheticTraffic.cc. The sequence of steps involved in generating and sending a packet are as follows.</p>

<ul>
  <li>Every cycle, each cpu performs a bernouli trial with probability equal to –injectionrate to determine whether to generate a packet or not.</li>
  <li>If –num-packets-max is non negative, each cpu stops generating new packets after generating –num-packets-max number of packets. The injector terminates after –sim-cycles.</li>
  <li>If the cpu has to generate a new packet, it computes the destination for the new packet based on the synthetic traffic type (–synthetic).</li>
  <li>This destination is embedded into the bits after block offset in the packet address.</li>
  <li>The generated packet is randomly tagged as a ReadReq, or an INST_FETCH, or a WriteReq, and sent to the Ruby Port (src/mem/ruby/system/RubyPort.hh/cc).</li>
  <li>The Ruby Port converts the packet into a RubyRequestType:LD, RubyRequestType:IFETCH, and RubyRequestType:ST, respectively, and sends it to the Sequencer, which in turn sends it to the Garnet_standalone cache controller.</li>
  <li>The cache controller extracts the destination directory from the packet address.</li>
  <li>The cache controller injects the LD, IFETCH and ST into virtual networks 0, 1 and 2 respectively.
    <ul>
      <li>LD and IFETCH are injected as control packets (8 bytes), while ST is injected as a data packet (72 bytes).</li>
    </ul>
  </li>
  <li>The packet traverses the network and reaches the directory.</li>
  <li>The directory controller simply drops it.</li>
</ul>

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</body>


</html>
